Smart cards contain a chip module, which is a carrier element for a chip/IC module, having electrically conductive contacts. These contacts are conductively connected to corresponding connection points of the chip, thus enabling the smart card to communicate with appropriate appliances (smart card terminals). The chip module is fixed in a cutout in the smart card body which is open towards the front side of the card. Such smart cards have already become very widespread in the form of phone cards, health insurance cards, GSM cards, bank cards and credit cards,
The layout of the surfaces of these smart cards (front side of the card and rear side) is configured in a complicated, mostly multicolored fashion; by contrast, at present only chip modules having a gold-colored or silver-colored surface of the contacts are available. In this case, these contacts are mostly constructed such that a metallic coating of nickel is applied as a diffusion barrier to a copper layer, and a gold, silver or palladium layer is applied thereon, the palladium metallic coating also appearing silver in color. So far, there have been very few possibilities for changing the optical appearance of the chip module surface.
A method for marking the metal contacts (applying visible information) of a smart card by laser engraving is described in EP 0 589 732. In this case, the gold layer is completely removed locally for the purpose of marking, the nickel layer situated therebelow, which is also partially removed as well, being visible. However, the associated damage to the gold layer impairs the protection of the metal contact surfaces against corrosion and oxidation.